1. Field of the Invention
The present invention relates to a signal transmission technique to transmit a signal between semiconductor devices.
2. Description of the Related Art
In recent years, a demand for a low-cost, high-speed and large-capacity information processing apparatus increases, and in accordance with the speed-up of the processing speed and the increase of the capacity, the speed-up of signal transmission is requested.
In a signal waveform transmitted by a signal transmission system, there is a problem of influence of rising/falling waveform blunting due to dielectric loss in a signal transmitting process in a lossy signal wiring, skin effect or the like. In a related art signal transmission system, when the load capacitance of a semiconductor device is large, there is a problem that a signal slew rate at the time of data writing becomes blunt, data transmission speed is decreased, and data transmission speed at the time of data reading is also limited.
Then, patent literature 1 (JP-A-2004-281960) discloses that in a signal transfer system, “A resistor R=Zpcb−Zpkg having a value of difference between characteristic impedances (Zpcb, Zpkg) of both wirings is inserted between an intermediate board wiring and a printed board wiring. At this time, an output impedance Rout of a driver of a signal transfer master and a signal transfer slave is made smaller than the intermediate board wiring impedance Zpkg, and an input impedance Rin of a receiver is made substantially equal to the intermediate board wiring impedance Zpkg.” By this, the signal is subjected to pre-emphasis and the slew rate is controlled.
However, in the invention disclosed in the patent literature 1, a consideration is not given to the difference between the characteristics of the semiconductor devices to transmit and receive a signal.
In the invention disclosed in the patent literature 1, when load capacitances at the time of data reading and writing of both the semiconductor devices are different, transmission speed may be limited to the transmission speed at which the signal can be transmitted to the semiconductor device having a large load capacitance. Besides, when a signal is transmitted to the semiconductor device having a small load capacitance, there arises a problem that ringing due to multiple reflection increases.